Mail processing systems for printing postage indicia on envelopes and other forms of mail pieces have long been well known and have enjoyed considerable commercial success. There are many different types of mail processing systems, ranging from relatively small units that handle only one mail piece at a time, to large, multi-functional units that can process thousands of mail pieces per hour in a continuous stream operation. The larger mailing machines often include different modules that automate the processes of producing mail pieces, each of which performs a different task on the mail piece. The mail piece is conveyed downstream utilizing a transport mechanism, such as rollers or a belt, to each of the modules. Such modules could include, for example, a singulating module, i.e., separating a stack of mail pieces such that the mail pieces are conveyed one at a time along the transport path, a moistening/sealing module, i.e., wetting and closing the glued flap of an envelope, a weighing module, and a metering module, i.e., applying evidence of postage to the mail piece. The exact configuration of the mailing machine is, of course, particular to the needs of the user.
Typically, a control device, such as, for example, a microprocessor, performs user interface and controller functions for the mailing machine. Specifically, the control device provides all user interfaces, executes control of the mailing machine and print operations, calculates postage for debit based upon rate tables, provides the conduit for the Postal Security Device (PSD) to transfer postage indicia to the printer, operates with peripherals for accounting, printing and weighing, and conducts communications with a data center for postage funds refill, software download, rates download, and market-oriented data capture. The control device, in conjunction with an embedded PSD, constitutes the system meter that satisfies U.S. information-based indicia postage meter requirements and other international postal regulations regarding closed system meters. The United States Postal Service (USPS) initiated the Information-Based Indicia Program (IBIP) to enhance the security of postage metering by supporting new methods of applying postage to mail. The USPS has published draft specifications for the IBIP. The requirements for a closed system are defined in the “Performance Criteria for Information-Based Indicia and Security Architecture for Closed IBI Postage Metering System (PCIBI-C), dated Jan. 12, 1999. A closed system is a system whose basic components are dedicated to the production of information-based indicia and related functions, similar to an existing, traditional postage meter. A closed system, which may be a proprietary device used alone or in conjunction with other closely related, specialized equipment, includes the indicia print mechanism.
The PCIBI-C specification defines the requirements for the indicium to be applied to mail produced by closed systems. An example of such an indicium is illustrated in FIG. 1. The indicium 10 consists of a two-dimensional (2D) barcode 12 and certain human-readable information 14. Some of the data included in the barcode can include, for example, the PSD manufacturer identification, PSD model identification, PSD serial number, values for the ascending and descending registers of the PSD, postage amount, and date of mailing. In addition, a digital signature is required to be created by the PSD for each mail piece and placed in the digital signature field of the barcode. Verification of indicium is performed by the postal service scanning a mail piece to read the 2D barcode and verifying the information contained therein, including the digital signature. If the verification is unsuccessful, indicating that the indicium may not be authentic, the mail piece may not be delivered.
Since postal services accept indicia printed by mail processing systems as conclusive proof of payment of the amount of postage indicated, such devices are in effect machines for printing money. As a result postal services have imposed high standards for the print quality of indicia images produced by such machines, to ensure that the postal verification equipment can properly read and decode the barcodes included in the indicium. Many postal services, such as, for example, the United States Postal Service (USPS), specify acceptable contrast ratios that must be provided between images printed on a mail piece and the mail piece for the images to be properly read. Even if an indicium is valid, if the verification equipment is unable to read the indicium due to poor contrast ratio or print quality, verification will not be possible. It is therefore necessary to ensure that the printing systems utilized by the mail processing systems are capable of consistently producing high quality images that have sufficient contrast with the background to increase the read rates of such images.
In recent years, ink jet printing systems have been utilized in mail processing systems. Ink jet printing systems, as used herein, includes any form of printing wherein print control signals control a print mechanism to eject ink drops to produce a matrix of pixels, i.e. picture elements, to represent an image. An ink supply, typically in the form of a reservoir, supplies ink to the print mechanism. In highly-controlled environments, e.g., on a single substrate matched to the printing method, it is possible to consistently achieve high quality prints that will achieve high barcode read rates. Mail processing systems, however, are not controlled environments, as printing will be performed on a variety of substrates, e.g., mail pieces, having different characteristics. Currently, the ink used in mail processing systems is manufactured to be as dark as possible to provide the greatest contrast with respect to a typical mail piece upon which an indicium will be printed, such as, for example, a white or off-white mail piece. For darker colored mail pieces or glossy mail pieces, however, the contrast between the ink used for printing and the background may be insufficient for the indicium to be properly read.
Thus, there exists a need for systems and methods for improving print quality on mail pieces that do not have sufficient contrast with the ink used to print an image to increase the read rates of images printed on such mail pieces.